Yieldable shroud support

ABSTRACT

A gas turbine has a stationary turbine rotor shroud of ceramic mounted on a metal ring. The mounting is resilient metal pins received in circular holes in the shroud ring and in radially extending slots in the supporting ring to allow relative radial expansion while centering the shroud ring with the turbine axis. The locating pins are slightly barrel-shaped and are slotted through the intermediate portion of the pins so they fit snugly in the ceramic but are yieldable to accommodate slight relative shifting or differential thermal expansion of the pin and shroud without imposing high local stresses on the ceramic material.

United States Patent 11 1 Ricketts 1 Aug. 26, 1975 [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: May 31, 1973 [21] Appl. No.: 365,444

OTHER PUBLlCATlONS Prodelin Inc., Catalog 595, Rigio 800, Kearny, NJ., 1959, p. 13.

United Kingdom 85/83 Germany 85/83 Primary Examiner-C. J. Husar Assistant ExaminerL. .1. Casaregola 52 us. c1. 415 134; 415 214; 85/83; Arwrney, Agent, or Firm-Paul Fitzpatrick 403/292 [51] Int. Cl. F01D 25/26; FOlD 25/28 57 ABSTRACT [58] Field of Search 415/214, 134, 135, 136; 1

60/3932; 403/2, 292, 337; 285/2, 3; 85/83; A gas turbine has a stationary turbine rotor shroud of 52/585 ceramic mounted on a metal ring. The mounting is resilient metal pins received in circular holes in the 5 References Cited shroud ring and in radially extending slots in the sup- UNITED STATES PATENTS porting ring to allow relative radial expansion while centering the shroud ring with the turbine axis. The locating pins are slightly barrel-shaped and are slotted 3232"160 2/1966 Fork ct aL 85/83 through the intermediate portion of the pins so they fit Smuland I I 4 I 4 4 I h snugly in the Ceramic but are tO accommo- 3451215 6/1969 Barr. 60/3932 date slight relative shifting or differential thermal ex- 3,635,577 1/1972 Dec 415/214 pansion of the pin and shroud without imposing high FOREGN PATENTS OR APPLICATIONS local stresses on the ceramic material. 723,505 2/1955 United Kingdom 415/214 2 Claims, 4 Drawing Figures P e /2\ A9 1 Z?" 1% A .5 l/ 7 y 7 YIELDABLE SHROUD SUPPORT My invention relates to turbines and to the mounting of ceramic parts, and to resilient support devices particularly suited for supporting a ceramic member without imposing destructive stresses on it.

More particularly, my invention is directed to an improved turbine structure in which the turbine rotor is disposed within a nonrotating ceramic shroud ring supported on the metallic structure of the turbine stator. The invention is directed to a supporting arrangement allowing for relative expansion of the shroud and its supporting support, and relative expansion of the connecting means between the shroud and support relative to the shroud.

Further, the invention is directed to a supporting pin which is readily fabricated to precise dimensions and which is of such resilient characteristics that it may be fitted snugly into a ceramic structure without imposing undue stresses on the ceramic notwithstanding differences in the coefficients of thermal expansion of the pins and the ceramic.

The principal objects of my invention are to improve the reliability and efficiency of a turbine, to provide a satisfactory means for mounting a ceramic shroud on a metallic turbine case structure, and to provide yieldable mounting pins of metal which fit snugly in a ceramic body and are yieldable to accommodate differential expansion without imposing undue stress on the ceramic.

The nature of my invention and its advantages will be clear to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention in connection with the accompanying drawings thereof.

FIG. 1 is a partial sectional view of a gas turbine taken on a plane containing the axis of rotation of the turbine rotor.

FIG. 2 is an elevational view of a mounting or locat ing pin.

FIG. 3 is a cross section view of the pin taken on the plane indicated by the line 33 in FIG. 2.

FIG. 4 is a longitudinal sectional view of the pin taken on the plane indicated by the line 44 in FIG. 3.

FIG. 1 illustrates a single stage turbine 2 comprising a rotor disk 3 fixed by welding or otherwise to a shaft 4. This shaft is rotatably mounted by a ball bearing 6 mounted in a shaft housing 7 and held in place by an annular retainer 8 secured to the shaft housing by a ring of cap screws 10. A turbine nozzle 11 comprises an outer shroud 12, a ring of vanes 14, and an inner shroud 15. The inner shroud is connected to the retainer 8 by a sheet metal ring 16 welded to both. Hot motive fluid gases generated in a combustion apparatus 18, only partially shown, are discharged through an annular outlet 19 of the combustion apparatus into the nozzle 11. The nozzle vanes direct the motive fluid onto blades 20 which may be integral with or fixed to the rotor disk 3, thus driving the turbine rotor 3. The rotor may be connected to a compressor (not illustrated) which supplies air to the combustion apparatus. The turbine 2 may discharge through an annular duct 22 into a further turbine (not illustrated) or into exhaust. An oil seal 23 engages the turbine shaft 4. The structure so far described will be recognized by those skilled in the art as conventional in its overall arrangement and will require no further explanation. Collman et al U.S. Pat. No. 3,267,674, Aug. 23, 1966, discloses an engine of this general type.

The gas flow through the turbine blades 20 is confined at the outer diameter of the rotor by a fixed shroud 24 of ceramic material which is located axially of the engine between the rear face of outer shroud 12 and the forward edge of the outer wall 26 of duct 22. A ceramic shroud ring may be of material of such thermal expansion characteristics that it expands about the same as the turbine rotor between cold, idle, and full power engine operating conditions.

To locate the shroud ring in the plane transverse of the axis; that is, to maintain it centered with the axis of rotation of the turbine, it is supported from the outer shroud 12 by a number of equally spaced mounting or locating pins 28. Preferably, there are six such pins disposed at angles around the turbine axis. Each pin 28 is received in a circular hole 30 in the shroud 24, each hole bottoming in an enlarged recess 31. The other end of each pin is mounted with freedom for movement radially of the turbine in a slot 32 machined in the rear face of nozzle shroud 12. With the six mounting points thus provided, the shroud 24 is centered and relative radial expansion of the shrouds l2 and 24 is accommodated by movement of the pins radially in the slots 32. Normally, it would be expected that the metallic shroud 12 has greater thermal expansion than ceramic shroud 24, because most ceramics have much lower temperature coefficients of thermal expansion than metal. However, the reason for the difference in expansion is relatively immaterial in this case.

The pins 28 are of special structure to accomplish the desired end of supporting the ceramic without imposing loads which might cause fractures of the ceramic, which ordinarily is a relatively brittle material. Referring to FIGS. 2, 3, and 4, each pin 28 is aslightly barrelshaped or fusiform body of basic hollow circular annular cross section. It comprises a first head 34 adapted to enter the slot 32, a central portion 35, and a second head 36 adapted to be received in the recess 31. Preferably, as illustrated here, the body is symmetrical about the central plane indicated by the line 33 so that the ends are interchangeable, but this is not necessarily the case. The central bore 38 extends the length of the body, serving to lighten the pin and to increase its flexibility as will be explained. The heads may be solid, but it is convenient and harmless to bore its entire length.

Four slots 40 tapering toward the interior of the pin extend the length of, or substantially the length of, the central portion 35; that is, essentially from one head to the other in the preferred form. These slots may be milled or otherwise provided, and need not necessarily be tapered. This leaves four mutually spaced struts 42 extending generally parallel from one head to the other.

In the preferred form illustrated, the basic exterior circle bounding the central portion is of very slightly greater diameter than the head 34, the difference being exaggerated in the drawings for clarity. In the specific example being described, the greatest diameter of the pin is 0.254 inches and the diameter of the head is 0.250 inch, the length of the pin being .75 inch and the length of each head .12 inches. To facilitate insertion of the pins, the ends of the heads are chamfered as indicated at 43. The pins are made of a heat resistant metal such as S.A.E. type 304 steel, which also has a desirably low coefficient of thermal expansion.

The circular hole 30 in the shroud is sized so that it is slightly smaller than the greatest diameter of the pin, the preferable difference being 0.0008 inch, varying somewhat due to tolerances. It is not desired that the pins have any clearance from the ceramic. They should be a slight interference fit. Because of the division of the pin into the four struts and the hollow center, the central part of the pin may be deflected radially inward sufficiently to fit into the hole without any significant stress on the ceramic, even though there may be some later expansion of the pins in service as the engine is heated. If there is also some warping of the shroud 24 or its support 12, the pins can be deflected slightly from their normal rectilinear axis to accommodate such distortions. Normally, however, the pins ride freely in the slots 32 and simply fit snugly in the holes 30.

It will be apparent that the number of slots 40 and struts 42, illustrated as four, is not critical; for example, there might be three, five, or six struts.

FIG. 1 also illustrates a containment ring 46 mounted around the exterior of the shroud 24, this ring being made of a number of layers of sheet metal rolled up into a ring. The containment ring is retained on an outer casing 47 of the turbine.

It should be apparent to those skilled in the art from the foregoing that I have devised a particularly suitable and satisfactory mode of locating and retaining a ceramic ring on a supporting structure involving a mounting or locating pin of novel structure particularly advantageous in such service.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

I claim:

1. A turbine stator structure comprising, in combina tion, a metallic support ring defining angularly distributed radially extending slots in a radial face of the ring; a shroud ring of ceramic material disposed adjacent to the said face; the rings being coaxial, and the shroud ring defining holes each confronting one of the said slots; and mounting pins each extending into a said slot and into the corresponding hole so as to position and support the ceramic shroud ring and tolerate relative radial expansion of the respective metallic and ceramic material rings, each mounting pin having a head at each end and having a central portion joining the heads, the central portion having longitudinal slots dividing it into at least three substantially equally spaced radially yieldable struts extending in generally parallel relation between the heads, the central portion extending into a said hole and being of such size as to have a slight interference fit therein to center the pin in the hole.

2. A turbine stator structure comprising, in combination, a support ring defining angularly distributed radially extending slots in a radial face of the ring; a shroud ring of ceramic material disposed adjacent to the said face; the rings being coaxial, and the shroud ring defining circular holes each confronting one of the said slots; and mounting pins each extending into a said slot and into the corresponding hole so as to support the shroud ring and tolerate relative radial expansion of the rings, each mounting pin having a head of circular external cross section at each end and having a hollow central portion of circular basic cross section joining the heads, the central portion having longitudinal slots dividing it into at least three radially substantially equally spaced yieldable struts extending in generally parallel relation between the heads, the diameter of the basic cross section circle of the central portion being slightly greater than that of the head received in the said hole and being sufficiently greater in diameter than the said hole to provide a slight interference fit therein, the central portion being fitted in the said hole. 

1. A turbine stator structure comprising, in combination, a metallic support ring defining angularly distributed radially extending slots in a radial face of the ring; a shroud ring of ceramic material disposed adjacent to the said face; the rings being coaxial, and the shroud ring defining holes each confronting one of the said slots; and mounting pins each extending into a said slot and into the corresponding hole so as to position and support the ceramic shroud ring and tolerate relative radial expansion of the respective metallic and ceramic material rings, each mounting pin having a head at each end and having a central portion joining the heads, the central portion having longitudinal slots dividing it into at least three substantially equally spaced radially yieldable struts extending in generally parallel relation between the heads, the central portion extending into a said hole and being of such size as to have a slight interference fit therein to center the pin in the hole.
 2. A turbine stator structure comprising, in combination, a support ring defining angularly distributed radially extending slots in a radial face of the ring; a shroud ring of ceramic material disposed adjacent to the said face; the rings being coaxial, and the shroud ring defining circular holes each confronting one of the said slots; and mounting pins each extending into a said slot and into the corresponding hole so as to support the shroud ring and tolerate relative radial expansion of the rings, each mounting pin having a head of circular external cross section at each end and having a hollow central portion of circular basic cross section joining the heads, the central portion having longitudinal slots dividing it into at lEast three radially substantially equally spaced yieldable struts extending in generally parallel relation between the heads, the diameter of the basic cross section circle of the central portion being slightly greater than that of the head received in the said hole and being sufficiently greater in diameter than the said hole to provide a slight interference fit therein, the central portion being fitted in the said hole. 